Radio echo detection system



y 8, 1956 E. H. B. BARTELINK 2,745,097

RADIO ECHO DETECTION SYSTEM Filed Oct. 50, 1945 A.T.R.

BOX I I2 |5 l lIs I6 I8 27 26 s A.T.R. I REcEIvER 7 BALANCED Q XYQY I BOX CHANNEL DETECTOR QCAMPUHER II T L I I9 2I 33 I TRANSMITTER ZKC.

AND MULTI- fig gg MODULATOR VIBRATOR To SERVO Io 20 I 24 MEcI-IANIsM ung PUSH-PULL VIBRATOR AMPLIFIER GATE KEYING IM.c. GENERATOR CIRCUIT OSCILLATOR lcu INVENTOR EVERHARD H. B. BARTELINK Q L DI LLC/LW Q ATTORNEY RADIO ECHO DETECTION SYSTEM Everhard H. B. Bartelink, Cambridge, Mass., assignor by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application October 30, 1945, Serial No. 625,665

7 Claims. (Cl. 343-11) This invention relates to object detectors, particularly those which emit a directed series of electromagnetic pulses and utilize the reflected energy from the object on which the pulses impinge to furnish an indication of the direction and range of the object.

Object detectors are already well known in the art and have been developed sufliciently to permit their use in gun laying where extreme accuracy is required. The present object detectors as used in gun laying use either conical scanning or multiple lobing. A conical scan system presents the mechanical difliculty of securing a sufficiently rapid scan to avoid losing a rapidly moving or fluctuating signal, such as from an aircraft. A multiple lobing system presents difliculty in balancing the overall gain of any two of the necessary plurality of receiver channels, particularly when the receiver gains are to be varied over wide ranges.

In the present invention a multiple lobing system is used, but a receiver is used having only one channel.

A unique switching means is provided for alternately connecting the receiver channel to the respective lobe paths in the antenna during reception of the reflected transmitter pulse to permit comparison of the energy received by the respective lobe paths. This will furnish an indication of the correction necessary in the direction of the antenna to permit training on the target. To secure suflicient switching during a transmitter pulse, a relatively wide transmitter pulse is necessary with a 1 resulting loss of range accuracy. This objection is overcome by alternating the wide pulse with a narrow pulse which is used only for determination of range.

It is an object of this invention to provide an object detector, which indicates accurately the direction and range of a fast moving object.

-It is a further object of this invention to provide an object detector using multiple lobing with a single receiver channel.

It is a further object of this invention to provide an object detector for use in the laying of guns or similar directive devices.

These and other objects will become more apparent upon consideration of the following description together with the accompanying drawing where:

Fig. 1 is generally a block diagram of an embodiment of the invention; and

Fig. 2 is a diagram of certain waveforms which occur in this embodiment.

The embodiment of the invention disclosed in Fig. 1 includes an antenna array which comprises a transmitting ,parabolic reflector type antenna in which the radio frequency energy is fed to a dipole located at the focal point of the parabola and two similar receiving dipoles with parabolic reflectors 11 and 12, all mechanically linked to move together as indicated by dotted line in either azimuth or elevation or both to permit simultaneous motion in the direction of an object to be detected. Dipole parabolic reflector antennas are called hereinafter by the name dish by which they are com Unimd fis Patent 2,745,097 Patented May 8, 1956 ice monly called. The receiving dishes have overlapping lobe patterns which enable the dishes 11 and 12 to impress equal amounts of energy on the receiving paths 13 and 14 corresponding to the respective lobes when the antenna is directed on the object, and different amounts when the antenna is directed off the object. Electronic antenna switches, known as anti-transmit receive (ATR) boxes, 16 and 17 are placed in respective paths 13 and 14 for alternately disconnecting the respective paths to a receiver channel 18 in response to triggering voltage applied thereto.

Block 19 represents a transmitter and associated modulator, which impresses either a long or short pulse of electromagnetic energy on the antenna, which is directed by dish 10 in the desired direction of emission. Multivibrators 20 and 21 are locked through the path joining their blocks to produce each a series of pips of a frequency of 1 and 2 kilocycles respectively, alternating pips of the higher frequency series coinciding in time with succeeding pips of the lower frequency series as shown by waveforms A and B in Fig. 2. Both series of pips are impressed on the modulator at 19 and combined therein to result in alternating large and small pips as shown by waveform C, a large pip occurring when pips of each series are coincident. The modulator is designed to trigger the transmitter in such a manner that it generates a relatively long pulse emission, say 10 microseconds, in response to the large pip and a relatively short pulse emission, say 1 microsecond, in response to the small pip. Thus a series of alternating long and short pulse emissions as shown by waveform E will be directed from the antenna in the desired direction of emission. Alternatively, the modulator may be arranged to produce short pulse emissions when A pips occur alone and long pulse emissions when A and B pips occur simultaneously.

An oscillator 22 having a period relatively short in relation to the duration of the long pulse emission is provided. With a 10 microsecond long emission pulse a frequency in the order of 1 megacycle for the oscillator is necessary. The output of the oscillator is fed through a keying circuit 23 to a push-pull amplifier 24, which gives a balanced amplified output having also a frequency of one megacycle. The pips from multivibrator 20 are utilized to trigger a gate generator 25 to produce a voltage gate as shown by Waveform D in Fig. 2. The voltage gate has a duration almost that of the period of the higher frequency multivibrator, which in the instant embodiment will be a few microseconds less than 500. The gate voltage controls keying circuit 23 to connect the output of oscillator 22 to amplifier 24 during occurrence of the voltage gate. One of the balanced outputs of amplifier 24 is led to each of the ATR boxes 16 and 17. When an ATR box is triggered by a positive voltage from amplifier 24 the corresponding antenna path 13 or 14 will be effectively disconnected. Thus receiving paths will be alternately disconnected at half microsecond intervals during the occurrence of the gate voltage from generator 25, which will also be the time that any reflected pulses of the long emission pulse are received. During reception of the long reflected pulse the output of receiver channel 18 will be a series of adjacent pulses of half microsecond duration, the relative heights of adjacent pulses corresponding to the amount of reflected energy received by each of the paths 13 and 14, which in turn depends on the direction of the reflecting object with respect to the antenna. The receiver channel output is fed to a balanced detector 27, already well known in the art, while the balanced output from amplifier 24 is also fed to this detector. Consequently at the output of balanced detector 27, a voltage wave will appear proportional to the difference in magnitudes of? the adjacent" half microsecond pulses in the receiver --channel--output, and-ofpolarit-y depending-on thedirection of deviation of thedirection of the antenna from that of the object. This voltage wave is rectified and is to beunclerstoo'd that the cathode ray tube has the .usualsweep and direction-"alignment circuits, which are not disclosed. When the="-antenna is directed on'the .5: reflectingobject, this'long reflected pulse will be indicated by 'a'trace 31in the formof aradial line on the'tube screen. The lengthof the trace will depend on the duratio nlof the-sweep withrefer'ence to the-duration of the v:.';pulse, and the :radial directionwilldepend on the direction of the antenna. When the antenna is directed off the reflecting object, 'cathod'e ray tube 30 will be cutoffztorender it inoperative and the trace will not appear. his true that for extreme deviations'in the antenna from the direction of the target, trace 31 would not appear 'iwith conventional circuits. "However; cathode ray tube iscutoff by-the circuit described above when only slight deviations occur. Hence" greater accuracy in determination of the direction of the target'is obtained by this circuit. Without the circuit, -trace 31 Would-have a 2 width. comparable'to the usual width of trace 32, which t-is the short reflected-pulse displayed on the tube screen.

- I Since intensifier grid 29 is connected with receiver channel 18 at all times, the short reflected-pulse will be impressed on the intensif ergrid of the scope alsol The :voltage gate from generator 25 is fed to full wave amplifier rectifier 28 to-unblankit and thus'render it operative only for the duration of the gate. any disturbance thatamplifier rectifier 28 would other- Hence wise produce on cathode ray tube 30 during reception of the short reflected pulses "is blanked out, and the object detector functions during this reception in conventionalmanner to present the trace of the short'pulse in a a position corresponding to the range and direction of the f-reflecting object? The-repetition rate for the shortpulses .is still sufliciently high for excellent operation. It is well established that' a short. transmitter pulse gives greater range accuracy: than adlong pulse. I Inasmuch as a short transmitterpulse is utilized here in conventionial manner for range': determination, the 'range accuracy of. this invention will be equal 'to' that of the object dertectorsiof the prior artw However, the-direction of the object willbe determined with much greater accuracy. If 2 desired the-outputof :balanc'ed detector 27 may be connected to aideviation' meter 33; which will indicate when the.-antenna istrained on and on theobj ectbeing dew'tected. -Also this output may be utilized to control a servo-mechanism to'train' guns in accordance with the wvoltage fed to the servo-mechanismlin a manner well 60 known in the art.

' 'It-isjto be understood that while only two receiving dishes have been" disclosed to-.'permit lobing in only one "plane which may be either azimuth or elevation, two

It is also to be understood that in-place of the plurality'of dishes disrclosed, 1av single reflector having dipoles arranged with ,-respect thereto to give the desir'edlobing Without undesirable couplingl'in"manner well known in the art 'c'oul 'be used.

The invention is to be limited only by the scope of the appended'claims.

What is claimed is:

1. An object detector of the type which transmits periodically recurring radio pulses and receives pulses which are reflections from said objects, comprising a directive antenna having overlapping receiving lobes, a transmitter, means for pulsing said transmitter to produce a 'series 'of long andshortpulseeinissions at different times, a receiver, .means for alternately disconnecting said receiving paths of said antennafror'n said receiver during the-reception of the reflection pulses produced by said long pulse, means forproducing a voltage having a 'mag'nitudedep'ending on the -dif-ference in the energy'in said reflection-pulses-ineach of said receiving paths, a cathode ray tube connected with said receiver for indicating said reflection pulsesproduced by said long and short pulses, and means for biasing said cathode ray tube beyond cutoff in response w said voltage.

2-. An'sobject detector, comprising 'adirect'ive' antenna having overlappingreceiving-lobes, a transmitter; means for pulsing the transmitter-toproduce a series of alternating long and short-pulse emissions from said antenna, a receiveremeans for-alternately disconnecting the --receiving paths of 'said antenna r corresponding to said {1 lobes' from said'receiver for-periodsrelatively short with respect to the duration'of the long pulse at timeintervals extending from the ernission-of the long pulse' toal'most thefemission of the succeeding short 'pulse'; =means connected witli' said receiver output for producing 'avoltage depending on the .relative magnitudes of the reflected "energy received in said 'pathsfro'm said long pulse emissions, a cathode raytub'e also connectedwith said receiver output for indicating the reception of 5 reflection pulses produced by said long andshort puls'es, and means for biasing"said"cathode ray "tube beyond cutoff in 1 response to said voltage.

=3. An obje'ct'detector; comprisinga directive antenna having overlapping receiving lobesj-a transmitter connected therewith, means for producing two series of voltag'peaks,

-. one-series beingiof a frequencytwicethat -"of theother,

alternate voltage peaks of said one series coinciding in time with succeedingvoltage-peaks of "said other series, said two-series of voltage pulse's' combining{to-produce alternating'large and small voltage-pulse,'-means for; triggering said transmitter in response to said large and small voltage pulses to produce a' series 'of anemann'g'ueng and short pulse emissions fromsaid-antenna,' a gating circuit for producing a-voltage'gate in response to the occurrence "of voltage pulsesof the lower frequency, said voltage gate having a 'duration almost that" of the period of the voltage pulses of the higher frequency, an o's'cillatcar'having a period'relatively short in relation Ito the duration 'of the long pulse emission;-'a"push-pullaihplifiei' for the amplifying of the output of said oscillator, a keying circu'it conalternately disconnecting the receiVing -pat'hsofsaid an- '-=tenna corresponding to each of said re'ce'iving lobes-from said receive1' c'hann'elin response to pdsitive'cycles of said oscillator output, a'fca'tho'de ray tube connecteifwith -the=output ofsaid rec'eiv'er chann el rar prese'nn the reflected energy of said short pulse inis sions in a position corresponding to the *rarige' and' 'difectionj of the" reflecting object, a balanced detector fed by the ioutpu'ts or said for rectifyin'g' the 'said detector" vqna efwave and'ioperative in response'to said gate voltage 't'o produce a voltage during sa'id gate depending on tl1ernagnitude of'said balanced detector-voltage wave'jmeans for impressing said A rectifier voltage on thecathode of said"'c'athode' raytube to bias said tube' beyon'd" cutoff in response 'to the deviation of the antenna from the direction of the reflecting object.

4. In a radio pulse echo object detection system of the type which transmits periodically recurring pulses of radio frequency energy in a series of alternately long and short time duration emissions and receives pulses which are reflected from objects, in combination, a directive antenna array having at least first and second dipole-fed parabolic reflector antennas mounted to have overlapping lobe patterns in a selected plane such that said antennas receive equal amounts of reflected energy from an object lying on the intersection of said lobes, a receiver, means including electronic switches for coupling each of said antennas to said receiver, a radio frequency oscillator,

means energized in synchronism with the transmission of each long time duration pulse to apply the output of said oscillator to said switches so that the receiver alternately carries signals from said first and second antennas separately during alternate switching cycles, a balanced detector responsive to said oscillator output and said receiver output signal to derive an output voltage having an amplitude related to the difference in energy received by said first and second antennas and a polarity indicative of the antenna receiving the greater amount of reflected energy, a cathode ray indicator connected to said receiver for displaying the output thereof, means for rectifying and amplifying said output signal, and means for applying said rectified and amplified output voltage to bias said cathode ray tube to cut-off, whereby said cathode ray tube is inoperative in the event said antenna array directive pattern deviates from the direction to said reflecting object and means energized 'm synchronism with the trans mission of each short time duration pulse to bias said amplifier to nonconduction, whereby said cathode ray tube indicator is operative during the reception of reflected pulses of short time duration.

5. In a radio pulse echo object detection system of the type which transmits periodically recurring pulses of radio frequency energy in a series of alternately long and short time duration emissions and receives pulses which are reflected from objects, in combination, a directive antenna array having at least first and second dispole-fed parabolic reflector antennas mounted for joint motion and arranged to have overlapping lobe patterns in a selected plane such that said antennas receive equal amounts of reflected energy from an object lying on the intersection of said lobes, a receiver, a transmission line including an electronic switch for each of said antennas for coupling said antennas to said receiver, a radio frequency oscillator, means energized in synchronism with the transmission of each long time duration pulse to apply the output of said oscillator to said electronic switches so that the receiver alternately carries signals from said first and second antennas separately during alternate switching cycles, a balanced detector responsive to said oscillator output and said receiver output signal to derive an output voltage having an amplitude related to the difierence in energy received by said first and second antennas and a polarity indicative of the antenna receiving the greater amount of reflected energy and an indicator responsive to said output voltage to show the deviation and direction of deviation of said antenna array from said object.

6. In a radio pulse echo object detection system of the type which transmits periodically recurring pulses of radio frequency energy in a series of alternately long and short time duration emissions and receives pulses which are reflected from objects, in combination, a directive antenna array having at least first and second dipole-fed parabolic reflector antennas mounted for joint motion and arranged to have overlapping lobe patterns in a selected plane such that said antennas receive equal amounts of reflected energy from an object lying on the intersection of said lobes, a receiver, a transmission line including an electronic switch for each of said antennas for coupling said antennas to said receiver, a radio frequency oscillator, means energized in synchronism with the transmission of each long time duration pulse to apply the output of said oscillator to said switches so that the receiver alternately carries signals from said first and second antennas separately during alternate switching cycles, a balanced detector responsive to said oscillator output and said receiver output signal to derive an output voltage having an amplitude related to the difference in energy received by said first and second antennas and a polarity indicative of the antenna receiving the greater amount of reflected energy, an indicator responsive to said output voltage to show the deviation and direction of deviation of said antenna array from said object, a cathode ray indicator connected to said receiver for displaying the output thereof, a rectifier for said output signal, an amplifier for said rectified output signal, and means for applying said rectified and amplified output voltage to bias said cathode ray tube to cut-oil, whereby said cathode ray tube is inoperative in the event said antenna array directive pattern deviates from the direction to said reflecting object.

7. In a radio pulse echo object detection system of the type which transmits periodically recurring pulses of radio frequency energy in a series of alternately long and short time duration emissions and receives pulses which are reflected from objects, in combination, a directive antenna array having at least first and second dipole-fed parabolic reflector antennas mounted for joint motion and arranged to have overlapping lobe patterns in a selected plane such that said antennas receive equal amounts of reflected energy from an object lying on the intersection of said lobes, a receiver, a transmission line including an electronic switch for each of said antennas for couplin said antennas to said receiver, a radio frequency oscillator, means energized in synchronism with the transmission of each long time duration pulse to apply the output of said oscillator to said switches so that the receiver alternately carries signals from said first and second antennas separately during alternate switching cycles, a balanced detector responsive to said oscillator output and said receiver output signal to derive an output voltage having an amplitude related to the diiference in energy received by said first and second antennas and a polarity indicative of the antenna receiving the greater amount of reflected energy, an indicator responsive to said output voltage to show the deviation and direction of devia tion of said antenna array from said object, a cathode ray indicator connected to said receiver for displaying the output thereof, a rectifier for said output signal, an amplifier for said rectified output signal, means for applying said rectified and amplified output voltage to bias said cathode ray tube to cut-0E whereby said cathode ray tube is inoperative in the event said antenna array directive pattern deviates from the direction to said reflecting object, and means energized in synchronism with the transmission of each short time duration pulse to bias said amplifier to nonconduction, whereby said cathode ray tube indicator is operative during the reception of reflected pulses of short time duration.

References Cited in the file of this patent UNITED STATES PATENTS 

